Take a look at the ad format samples on the Adsense site and you will see a bunch of squares and rectangles filled with ads, most of those ad units will contain more than one ad, on those units that do contain just the one ad, like the button or the half-banner, the ad will fill the space neatly and look pretty subtle.

You might be surprised if you put a skyscraper or a leaderboard on your site and find just one giant ad, written in super-sized text, all the effort you have put into picking the right ad for your site, testing to see which formats work best, and calculating which will give you the most clicks will have gone right out of the window, you have prepared your site to serve multiple ads that look like content, and instead you are handing out a single ad that just screams “Do Not Click Me”.

This can happen sometimes, but it’s not a reason to panic, it might even be a reason to celebrate, there are two possible reasons that Google is sending you these expanded text ads, the first possible reason is that you have been keyword-targeted, Google keeps track of your results and tries to serve up the number of ads for your page that will bring in the highest amount of income, that might be four ads in a unit, or just the one.

If I see that Google is giving me one ad, I will compare the results for that one ad to the previous results that I have had serving multiples ads in the same unit, if I find that my revenues have dropped I can either block that ad using my filters or just ask Adsense not to give me any more single ads, but I find that the expanded text ad is giving me more money, I might still be worried, I know that users are more likely to click ads that look like content, I also know that they prefer to have a choice of ads rather than just one option, if I am getting more clicks with just one ad, it could well be that I have been doing something wrong with that ad unit in the past, I would want to look at how well it’s been optimized and whether it’s in the right place to bring in the best income.

It could well be that this single ad is high-payer and works better with little competition, but it could also be that getting that one ad is a warning that something was wrong with the way you have laid out that ad unit on your site, you might want to try some different strategies to see if they will increase your revenues when the multiple ads come back.

There is another possibility though, you might have been site-targeted, this is a whole different history, it means that an advertiser has spotted your site and asked Google to run their ads on it on a pay per impression basis, you are no longer dealing with tempting people to click, so you do not care how much your ad looks like an ad, in fact you might even want it to look like an ad, if that’s what will keep the advertiser happy.

The most important point to bear in mind here is that you want to make sure that you are not losing money, it might be very nice for the advertiser to have exclusive control over a particular spot on your page but if you can make more money serving CPC ads in that space, you need to make sure that your site is working for you and not for the advertiser, again watch your stats for a week and see if the revenues you receive for your impressions are higher than those you receive for your clicks.